squishy

The 4x fuel burner engine also can't support much weight Btw, can you fix it so you can only attach something one way on the decoupler? Now if you put it 1cm too high it'll explode

You might be right, but if the simplest rockets it the most efficient, you might as well not build larger ones

True, however the medium fuel engine is WAY more powerful than the normal once. Also the new big fuel engine is way less powerful than the normal one. With powerful I mean it reaches way higher speeds/altitude with the powering the same rocket

These new parts are over powered :-X. I just snapped 4 medium sized fuel rockets and 4 long tanks (1.08) to my commandpod/SAS and it allowed me to reach escape velocity EASILY (4500m/s) straight up. This 11 part rocket goes faster and further than my 10-stage rocket from the default KSP :